The ever increasing search for oil and natural gas, as well as other subterranean deposits, has provided many and varied types of drilling rigs. Conventional drilling rigs utilise what is known in the drilling art as a "Kelly" system for rotation of the drilling bit. Other systems utilize what is commonly referred to as a "spinner", which is attached below a non-powered swivel to rotate a drill bit attached to a plurality of longitudinally coupled lengths of drill pipe in order to form the borehole. The drilling operation further requires means for providing drilling mud to the rotating drill bit in order to cool and lubricate the bit, as well as to remove particulates from the borehole. When a power swivel is utilized as will be defined within this specification, the swivel serves the further function of exerting pressure on the drill bit in order to assist its passage through the subterranean deposits.
Downward pressure exerted on the drill bit by a power swivel causes an associated reverse force to be exerted on the power swivel with the result that the power swivel drive system must be capable of accommodating this force. Furthermore raising of the power swivel and the attached lengths of drill pipe causes a reversely directed force to be applied to the power swivel with the necessity, therefore, of providing means integral with the power swivel, for accommodating these upwardly and downwardly directed forces.
While the power swivel requires means for accommodating the axially directed forces, it is also necessary that the length of the power swivel be minimized in order that a sufficient number of longitudinally coupled lengths of drill pipe may be connected to the power swivel and to those lengths of drill pipe already suspended in the borehole. It should be obvious that as the length of the power swivel increases, then the number of lengths of coupled drill pipe must decrease or the drilling rig mast or derrick height must be increased, which is not desirable. Consequently it is important that the power swivel drive system be as compact as possible in order to allow the maximum number of coupled lengths of drill pipe to be accommodated.
Conventional drilling rigs, particularly vertical drilling rigs, require at least an upper tong to be secured to the mast assembly in order to hold the lengths of drill pipe prior to coupling with the power swivel A means integral with the power swivel for holding the coupled lengths of drill pipe should advantageously effect the efficiency of the overall drilling operation.
A power swivel should be capable of being utilized by vertical drilling rigs as well as drilling rigs which are angularly displaceable around an axis. Such a universal power swivel requires a pressurized lubrication system in order to permit its use at any angle from the horizontal to the vertical.
Efficient creation of a borehole requires precise control over the rotational speed of the advancing drill bit. The speed of the rotating drill bit should be indepentently controllable relative to the longitudinal displacement of the power swivel.
The present invention provides a compact power swivel having a compact power swivel drive system driven by an electric motor whose rotational speed may be controlled by varying the current supply to the motor. Furthermore, the present invention discloses and claims a unique thrust bearing assembly designed to accommodate the radial and axial forces caused by reciprocal advancement and removal of the power swivel.
The present invention further discloses a disc brake which is utilized to lock the drill strap in a particular, predetermined position. This is necessary for establishing the correct orientation of the tools at the end of the drill string prior to start of drilling procedures, especially with directional drilling. Additionally the present invention discloses a system for providing drilling mud through the power swivel in order to lubricate and cool the drill bit. Finally, the major components of the present power swivel are secured to a removable mounting bracket in order to permit ready replacement of the power swivel components in the event of failure of one of the components, without the necessity of removing the entire power swivel assembly from the drilling rig mast. The present invention therefore overcomes the drawbacks and disadvantages of prior art power swivels and yet provides a compact power swivel adapted for both vertical and angular positioning.